1. Field of the Invention
The present invention relates to pressure relief apparatus and, more particularly, is directed to pressure relief doors for combustion vessels.
2. Description of the Invention Background
A variety of industrial systems exist wherein a pressurized liquid or gaseous medium is contained therein. For example, industrial boiler systems used to create steam for heating facilities must accommodate water and steam at varying temperatures and pressures. The pressure within those systems can, at times and for a variety of reasons, reach a magnitude wherein it must be reduced to prevent equipment damage and/or injury to personnel. Thus, a variety of valves and pressure relief apparatuses have been developed to permit the pressure to be relieved from the system when it reaches a potentially harmful magnitude.
Another industrial system that must be equipped with pressure relief apparatus is the combustion chamber that is used in connection with a number of different heating apparatuses such as furnaces and incinerators. Because those combustion chambers are typically used to burn a variety of different materials, some of which may be explosive in nature, it is possible for explosions to occasionally occur within the chamber. Such explosions cause a rapid increase of pressure within the chamber such that, if the excessive pressure is not relieved therefrom, the chamber could rupture and possibly injure personnel that are in the general vicinity of the incinerator. It is for that reason that the National Fire Protection Association (the "NFPA") requires incinerators to be equipped with apparatus adapted to quickly and safely relieve excessive combustion chamber pressures resulting from explosions occurring therein. In particular, NFPA regulations require the unit's primary combustion chamber to be equipped with a vent opening that provides at least one square foot of relief area per one hundred cubic feet of combustion chamber volume.
In incineration applications, in order to achieve proper temperature control within the combustion chamber to thereby ensure complete combustion of the material and to prevent the smoke and volatile gases that are created during the combustion process from leaking into the atmosphere, the combustion chamber must be maintained in an airtight condition. As such, in addition to being able to quickly and safely relieve excessive pressure from the combustion chamber, pressure relief apparatus used in connection with incinerators must also be capable of maintaining the airtight integrity of the combustion chamber under normal incineration pressures.
To address such concerns and requirements, a variety of explosion relief doors have been developed for use in connection with heating units and incinerator combustion chambers. For example, Weyenberg et al. U.S. Pat. No. 2,517,816 discloses an explosion relief door that is hingably attached to the combustion chamber such that it can swing open in response to an increase of pressure within the chamber. After the pressure has been relieved from the chamber, the door, by virtue of gravity, returns to a closed position. That apparatus, however, fails to provide means for maintaining an airtight seal between the door and the chamber when the door is in the closed position.
Another pressure relief door arrangement is taught in Ayers U.S. Pat. No. 2,623,482. The pressure relief door disclosed therein is adapted to cover a vent opening provided in the heating unit. The door is pivotally received on the lower portion of the opening and is equipped with a counterweight portion that serves to maintain the door in a closed position. An excessive amount of pressure within the unit will cause the door to pivot to an open position and thus relieve the pressure therefrom. After the excessive pressure has been relieved from the unit, the counterweight causes the door to pivot to a closed position. That pressure relief door is also not equipped with sealing apparatus that is capable of achieving an airtight seal between the door and the unit when the door is in a closed position.
To address such air leakage concerns, some incinerator pressure relief doors have been equipped with gasket seals that serve to provide an airtight seal between the door and the chamber when the door is in the closed position. However, as those gaskets begin to wear, air is permitted to enter into or pass out of the combustion chamber thus making it difficult to control the temperature therein.
Other incinerators are provided with pressure relief through their ash removal apparatus. In particular, some incinerators are equipped with a liquid filled trough at one end that is adapted to collect ash material therein. The end of the incineration chamber extends into and below the surface of the liquid to create a barrier to prevent air flow into or out of the incineration chamber. As the ash accumulates in the trough, it can be removed therefrom without disturbing the incineration process. In addition, trough arrangement also provides a means for relieving excessive pressures from within the combustion chamber. For example, a rapid increase in pressure caused by an explosion within the chamber will cause the displacement of the liquid and thereby permit the excessive pressure to exit the chamber. That arrangement, however, is not necessary for incinerators wherein frequent ash removal is not required.
Other sealing apparatuses and arrangements have been developed for achieving a seal between a door and a combustion chamber or heating unit. For example, the seal arrangement disclosed in Van Ackeren U.S. Pat. No. 4,016,045 applies a vacuum between the door and the oven to channel away any gas that may leak from the oven. Conversely, Beck U.S. Pat. No. 4,054,411 discloses a furnace door seal wherein a sealing gas is introduced between the confronting surfaces of the door and the oven to establish a gas barrier to prevent the combustion gases from leaking into the atmosphere. Both of those sealing arrangements, however, could have an adverse affect upon the stability of the pressure within the heating unit by either adding foreign gas into the unit or withdrawing combustion gas from the unit which could be hazardous.
Yet another sealing arrangement is disclosed in Schulte U.S. Pat. No. 4,284,479. The sealing arrangement includes a door body having an inner peripheral face that is arranged to confront a door frame provided around an opening in the oven. When in a closed position, the door body faces the door frame and is spaced therefrom to provide a channel for receiving a fluid sealing medium such as loam or coking duff that is injected therein. However, each time the door is opened, the sealant material must be cleaned from the door frame so that new material may be injected into the channel after the door has been closed. Therefore, this sealing arrangement would be ill-suited for incinerator applications wherein it is desirable for the relief door to quickly re-achieve an airtight seal between the door and the combustion chamber after an excessive amount of pressure has been relieved therefrom.
Thus, there is a need for a pressure relief apparatus that is capable of quickly relieving excessive amounts of pressure from an enclosed vessel such as a combustion chamber for an incinerator and that is also equipped with sealing apparatus that is capable of quickly re-achieving and maintaining the airtight integrity of the vessel after the excessive pressure has been relived therefrom.